Coupling Effects of CO2 and Thermal Treatment on the Rheological Behavior of Heavy Oil: An Integrated Experimental and Modeling Study.

The rheological behavior of high-viscosity heavy oil is crucial for its efficient development. CO2-assisted thermal recovery serves as an effective method to enhance heavy oil mobility. However, existing studies still lack sufficient quantitative characterization of the coupling effect of thermal and CO2 interactions on improving heavy oil flow capacity. To address this issue, this study thoroughly investigates the synergistic viscosity reduction mechanism and the evolution of rheological properties during heavy oil extraction under combined CO2 and thermal effects. Through systematic rheological testing and theoretical modeling, a modified Arrhenius model incorporating a shear correction factor was developed, enabling accurate prediction of the viscosity-temperature relationship under different shear rates. Dual hysteresis loop analysis was employed to quantify the effects of thermal and shear history, confirming that the thixotropic recovery capability of heavy oil is governed by both thermal and shear history and revealing an exponential decay pattern of thixotropic strength with increasing temperature and shear rate. A temperature-dependent Bingham constitutive equation was established, achieving precise prediction of rheological behavior across the full temperature range from the non-Newtonian to the Newtonian regime. This study elucidates the spatiotemporal evolution of heavy oil rheological behavior throughout the entire CO2-thermal synergistic extraction process, providing a key theoretical tool for accurate prediction of development performance and dynamic regulation of production parameters.